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/* 
{
  default () {},
  a1: 'abc',
  a2 () {},
  a3: 12,
  a4: 23
}
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    import {a1, a2, a3, a4} from './a.js'
    // 默认引入
    import aa from './a.js' // 是下面方式的简写
    import {default as aaa} from './a.js'
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